Recently, from the perspective of environmental protection, a wind turbine generator using wind power and other wind turbine generator using renewable energy such as tidal current, ocean current and river current are becoming popular. In the renewable-energy type power generating apparatus, motion energy of wind, tidal current, ocean current or river current is converted to rotation energy of the rotor and the rotation energy is converted to electric power by a generator.
This type of power generating apparatus requires a step-up gear between the rotor and the generator as the rotation speed of the rotor is smaller than the rated rotation speed of the generator. Specifically, the rotation speed of the rotor is increased by the step-up gear to the rated rotation speed of the generator and then inputted to the generator.
To improve power generation efficiency, the power generating apparatus of renewable energy type becomes larger to improve power generation efficiency and the step-up gear becomes heavier and more expensive as well. In view of this, a power generating apparatus of renewable energy type which uses hydraulic transmission having a hydraulic pump and a hydraulic motor instead of the mechanical step-up gear, receives increased attention.
For instance, Patent Literature 1 proposes a wind turbine generating apparatus which transmits rotation energy of the rotor to a generator via a hydraulic transmission.
With the use of the hydraulic transmission in which the hydraulic pump and the hydraulic motor are connecting by hydraulic piping, the freedom of arranging the transmission mechanism for transmitting rotation energy of the rotor to the generator is significantly improved. Thus, unlike a conventional wind power generating apparatus, it is not necessary to arrange all the transmission mechanisms within the nacelle installed atop the tower and it is possible to arrange the hydraulic motor and the generator connected to the hydraulic motor at ground level or seal level. This reduces load supported by the tower and reduces an installation cost of the wind power generating apparatus. In addition, it is easier to perform the maintenance of the hydraulic motor and the generator.
For instance, Patent Documents 2 through 5 disclose the wind power generating apparatus in which the hydraulic motor and the generator are arranged at ground level.
However, a general wind power generating apparatus rotates the nacelle depending on a wind direction in view of improving the power generation efficiency. Thus, whether the hydraulic motor and the generator are arranged at ground level or seal level, it is desired to design the wind power generating device capable of turning the nacelle.
Patent Literature 6 discloses a wind power generating apparatus in which the hydraulic motor installed at a bottom of the tower turns around a vertical shaft with the nacelle.
Patent Literatures 7 and 8 discloses a wind power generating apparatus in which a part of the hydraulic piping (a high-pressure oil passage and a low-pressure oil passage) connecting the hydraulic pump installed in the nacelle and the hydraulic motor installed at the bottom of the tower turns with the nacelle. In the wind power generating apparatus of Patent Literature 6, a hydraulic swivel arranged at a nacelle bottom turns the hydraulic piping on the nacelle side with the nacelle (as shown in FIG. 7 of Patent Literature 7 and FIG. 7 of Patent Literature 8). The hydraulic swivel consists of an outer part and an inner part which are rotatable relative to each other. The piping provided in the inner part is in communication with a loop passage provided at an inner periphery of the outer part.